1. Field of the Invention
This invention relates to a hybrid automobile provided with an internal combustion engine and electric motor.
2. Description of the Relevant Art
For an engine carried on an automobile or the like, torque and revolution number (RPM) characteristics over a wide range are required so that the engine may operate in any running condition (constant speed, acceleration, uphill road driving and so forth). Generally, the torque and the RPM's of the engine in which the fuel consumption efficiency is high are specified to a range peculiar to the engine. Therefore, there has been proposed a hybrid car including both an engine and a generator-motor so that the drawbacks of one of the power sources may be made up for by the benefits of the other power source under various conditions. Therefore, the overall energy efficiency of the car is improved.
In a conventional hybrid car, the engine is designed with a reduced capacity and is normally operated only in a range in which it exhibits a high fuel consumption efficiency. A motor controlling apparatus for a hybrid car is provided which effects regenerative control such that, when the car is accelerated or runs on an uphill road or the like, driving of the generator-motor is controlled with supplied power from a power supply such as a battery to make up for an insufficient driving torque. When the output of the engine exhibits some surplus power, generated energy, obtained when the generator-motor is driven by the engine, is regenerated into the power supply such as a battery (see the official gazette of Japanese Patent Publication Application No. 62-27604).
The conventional motor controlling apparatus for a hybrid car causes motor current to flow through the generator-motor and controls the generator-motor so that an aimed torque, calculated based on an operation amount of an accelerator pedal or the like, and a fed back driving wheel torque, detected by a torque sensor or the like, may be equal to each other to make up for an insufficient driving torque.
However, with the conventional motor controlling apparatus for a hybrid car, since the torque of the driving wheel, detected using a torque detection mechanism which has some range of mechanical dispersion, is fed back to cause motor current to flow though the generator-motor to make up for an insufficient driving torque, particularly when a high torque is requested while the speed of revolution is low, excessive motor current sometimes flows within the range of the dispersion. The excessive motor current may exceed a rated motor current and possibly damage the generator-motor and reduce its life. In order to prevent damage to the generator-motor, a generator-motor having a high rated motor current, taking an excessive motor current when a high torque is requested during low speed revolution, must be employed. Such a generator-motor has an increased size.